Piezoelectric ceramics have significantly contributed to downsizing and sophistication of electronic devices. In addition to applications to conventional devices such as sensors or ultrasonic transducers, piezoelectric ceramics are recently used, for example, as a raw material of transformers for LCD backlights of personal computers or a raw material of head parts of ink jet printers.
Lead-based materials such as PZT-based materials prevail nowadays as such piezoelectric ceramic devices. However, lead-based materials contain large amounts of harmful lead oxide, and thus, for example, environmental pollution by spilled lead oxide on disposal has been a matter of concern. Therefore, development has been strongly demanded for lead-free piezoelectric ceramic materials which can be used for alternatives to conventional lead based materials.
Recently, alkali niobate piezoelectric ceramics draw attention as lead-free ceramic materials, which exhibit relatively high piezoelectricity. Patent Document 1, for example, proposes a piezoelectric ceramic including a solid solution mainly composed of lithium sodium niobate, together with minor components as aluminum oxide and iron oxide. Patent Document 2 proposes an improved composition for a piezoelectric ceramic, which includes potassium niobate and sodium niobate, as main components, and copper, lithium, and tantalum, as additional components.
As a method of producing such piezoelectric ceramics, a method called a solid phase method has been widely known. The solid phase method typically includes mechanically mixing or kneading plural kinds of particulate materials as raw materials, then pelletizing, and calcining the obtained pellets.
In recent years, liquid phase methods of synthesizing NaNbO3 particles have also been studied. For example, Non-Patent Document 1 reports a method of synthesizing NaNbO3 particles by reacting NaOH or KOH solution with Nb2O5 particles.
Another technique has been recently reported on a method for producing particulate KNbO3 by once synthesizing layered K4Nb6O17 particles, and then heating the particles at a high temperature in a molten salt (Non-Patent Document 2).